Variable ramp for magnetrons



June 5, 1951 C, v, |TTQN l 2,555,349

VARIABLE RAMP FOR MAGNETRONS 2 Sheet's-Sheet l Filed Aug. 18, 1948 1N VEN TOR.

N m 7 L K w on Hh C June 5, 1951 Q v L11-TON 2,555,349

VARIABLE RAMP FOR MAGNETRONS l Filed Aug. 18, 1948 i 2 sheetssheen 2QLLQ?.

Patented June 5, 1951 UNITED STATES PATENT CFFICE VARIABLE RAMP FORMAGNETRONS Charles V. Litton, Redwood City, Calif.

Application August 18, 1948, Serial No. 44,869

7 Claims.

My invention relates to electron discharge devices and is particularlydirected to improvements in construction of devices of the magnetrontype.

In magnetrons and other centimeter-wave generators, the problem persistsof efliciently coupling the generator to its load circuit. Generally thelow impedance of a resonant cavity must be matched to the relativelyhigh impedance of the connected transmission line, and in the centimeterwave range, where the line usually comprises a wave guide, the end ofthe wave guide must be terminated at a relatively narrow slit in theside of the cavity. Accordingly, the junction between the wave guide andthe cavity must account for the difference in physical dimensions of thewave guide and cavity slit as well-as the difference in impedance of thetwo. Although the physical dimensions of a coupling circuit may becalculated for a particular set of operating parameters, any variationfrom those parameters, such as changes in frequency or changes inimpedance of the wave guide, causes a mismatch and ineicient operation.

'I'he principal object of my invention is an electrically efficientadjustable coupling between the resonant cavity of a centimeter wavegenerator and the output or load circuit of the generator.

A more specific object of my invention is an improved coupling structurebetween a resonant cavity and a wave guide which will accommodate greatdiierences in physical dimensions and which will match the impedances ofthe cavity and wave guide.

A still more specic object of my invention is a coupling between amicrowave generator Vand a load circuit, the impedance ratio of thecoupling being adjustable.

According to the invention there is provided a two conductortransmission line or wave guide for interconnecting an opening in aresonator and a larger output window, in which at least one of theconductors is pivotally supported, to

vary the transfer impedance of the line or guide.

2 tube is a tapered transmission line or wave guide extending fromopposite sides of the resonator opening to opposite sides of the window.The spacing between the conductors of the transmission line increasesthroughout the length of the line so that the inductance and capacity ofthe line varies with distance from the end of the line. Such a linepresents different impedances, respectively, to the resonator at one endand to a connected wave guide at the other end and may be easilyadjusted accurately to match the impedances for the efficient transferof energy from the cavity to the wave guide. Adjustment of the ratio ofimpedance transformation is made by moving one conductor of thetransmission line with respect to the other.

These and other features and objects of this invention and the manner ofattaining them will become more apparent and the invention itself willbe best understood, by reference to the following description Vof anembodiment of the invention taken in conjunction with the accompanyingdrawings, wherein:

Fig. 1 is a longitudinal sectional View of said one embodiment,

Fig. 2 is a cross sectional view of line I-l of Fig. l of said oneembodiment of the invention,

Fig. 3 is a view in perspective, of the adjustable conductor of thetransmission line of my invention, and taken on line 3-3 of Fig. 1,

Fig. 4 is an exploded view of the conductor of mig. 3. Y

The electron discharge device to which my invention applies comprises amicrowave generator with a cavity resonator and withV an opening in theside Wall of said cavity. To the side wall is hermetically joined theend of a tube, the

The particular microwave generator chosen for illustrating my inventionis a magnetron comprising, as shown in the drawing, a round solid metalanode structure I having a plurality of resonators formed by vanes 2arranged symmetrically about the central bore 3 and forming uniformlyspaced slots 4 communicating with the cavities. Electric oscillationsare induced in the slots and the cavities by electrons spiraling aboutthe cathode sleeve 5 supported along the center of the structure. Theend structures including the magnet poles, seals and cathode and heaterleads may be conventional and are not shown.

To remove high frequency energy from the magnetron, a slit 6 is made inthe side of one of the resonators, and to the side of the anodestructure is formed and hermetically joined one end of a drawn sheetmetal tube l. The tube may be rectangular or round, depending on thecross sectional shape of the wave guide 8 to be connected thereto.Should the anode be smaller in outside diameter than the wave guide, theanode end of the tube must of necessity be drawn in to join with theanode. While the tube must be open for the longitudinal transfer ofenergy. it must be sealed hermetically to gas to permit evacuation ofthe discharge space within the anode structure. A non-metallic Window 9of low-loss material, such as mica or hard glass, is sealed in the tube,preferably across the outer end. The sealing ring I0, after junctionwith the Window has been made, may be braZed to the end of the envelope.The shoulder II on the ring provides a snug sliding contact with the endof the wave guide into which my novel discharge device must feed highfrequency energy.

To summarize, the principal function of the tube is merely to enclosethe space between the magnetron and its wave guide, the size and shapeof the tube being determined principally by the sizes and shapes of themagnetron and wave guide. The internal configuration of the tube issubstantially independent, according to my invention, of the highfrequency parameters of the system. Hence the tube may be inexpensivelydie drawn or otherwise fabricated from sheet metal without troublesomedimensional tolerances.

Now, according to an important feature of my invention, a taperedtwo-conductor transmission line is incorporated within the tube toconduct the high frequency energy from the slit in the resonator to therelatively widely spaced sides of the wave guide. The two conductors I2and I3 of the line have opposed coextensive curved metal surfaces Iiiand i5 which in width may be equal to or less than the length of thecavity slit 6. For reasons which will more fully hereinafter appear, thespacing between the curved surfaces of the conductors of the line varieswith distance from one end of the line in such a way the inductance an-dcapacity of the line is an exponential function of said distance. It canbe shown, then, that the ratio of the impedance of the transmission lineat one end to the impedance at the other end is equal to where Zz and Z1are, respectively, the characteristic impedances of the line lookinginto the wide end and the close-spaced end of the line. The ratio ofimpedances are also equal to where e is the constant 2.718, l is thelength of the line, and )l is the variable cut-off wave length atvarious points along the line.

Hence, since the ratio of impedances presented to the resonator and tothe wave guide deponds upon the difference in spacing between conductorsat the ends of the line, the ratio of impedances may be changed byvarying the ratio spacings at the ends. According to a further andimportant feature of my invention this ratio of end spacings may bevaried, without appreciably disturbing the exponential relationship, bypivoting one of the conductors about a point near the wide spaced end.By moving the other end toward or away from the second conductor, thedesired impedance transformation is easily obtained` and the outputimpedance of my magnetron may be matched to the impedance of any waveguide.

As shown in the drawing, one transmission line conductor I3, is a solidblock of metal secured 4 to one wall of the envelope, the inner face ofthe block being machined to the exponential curvature mentioned. Theother conductor, I2, is similarly shaped and secured opposite the solidconductor, but is provided with a wide and relatively deep groove Iii,Fig. 4, throughout the length of the face of the conductor. Within thegroove is fitted a rectangular metal bar Il the outer face being formedwith the exponential curvature of the solid conductors. The bar ispivoted on pin I3 near the outer end by a pin driven through alignedholes in the block and bar. The position of the other end is xed by alink I9 hinged to a second pin 2c and extending to and through aflexible diaphragm 2|. The diaphragm is sealed by bra-zing to the link,and is seated in and joined gas tight around its periphery to thebell-shaped diaphragm support 22. The link and connected bar is movedagainst the yielding pressure of the diaphragm by the dial 23 which isscrew threaded at 24 over the support. The root spacing of theconductors of the transmission line may thus be varied in such a way asto preserve the exponential characteristic, and a broadband variableratio transformer is the result.

For electrical continuity between the grooved conductor and its bar,small coil springs 25 may be laid in slots in the sides of the bar andcompressed laterally between the inside conductor walls and the bar.

While I have described above the principals of my invention inconnection with specic apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention.

I claim: n

1. In a coupling device for an ultra high frequency transmission systemcomprising a tubular housing, a pair of elongated conductors disposedopposite each other within and lengthwise of said housing, the opposedsurfaces of said conductors being spaced apart with the spacingincreasing exponentially over at least a part of the length of saidconductors, one of said conductors being provided with a movable partincluding at least a portion of the surface thereof which opposes theother conductor and means for adjusting said movable part to vary thespacing between the said opposing surfaces of said conductors.

2. In a coupling device according to claim 1, wherein said one conductoris provided with pivot means located adjacent one end thereof forpivotally connecting thereto said movable part.

3. In a coupling device according to claim 1 further including anadjustable stem extending through a side wall of said housing, the innerportion of said stem being connected to said movable part and the outerportion of said stem being provided with means for adjusting theposition of said stem transversely of said housing, and means forpivoting said movable part at a point spaced from said stem.

4. In a coupling device according to claim 1, wherein said one conductoris channeled along the surface thereof facing said other conductor andsaid movable part is disposed in said channeled portion.

5. In an ultra high frequency transmission system having an ultra highfrequency generator of the resonant cavity type with an output slit in acavity wall thereof, a dielectric wave guide and a coupling devicedisposed between said output slit and said dielectric guide; saidcoupling device being characterized in that it comprises a tubularhousing and a pair of oppositely disposed conductors disposedlongitudinally of said housing from adjacent said slit to the input endof said guide, the opposing surfaces of said conductors being curvedaway from each other for at least part of the length thereof and meansfor varying the position of at least part of the said surface of one ofsaid conductors relative to the opposed surface of the other conductor.

6. In an ultra high frequency transmission system according to claim 5,wherein the movable part of said one conductor is provided with a pivotconnection adjacent the end of said dielectric guide and the means forvarying the position of said part includes an adjustable member foreiecting pivotal movement of said part.

7. In a coupling deviceaccording to claim 5,

6 wherein said one conductor is channeled along the surface thereoffacing said other conductor and said movable part is disposed in saidchanneled portion.

' CHARLES V. LITTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,200,023 Dallenbach May '7, 19402,409,913 Tonks Oct. 22, 1946 2,421,912 Spooner June 10, 1947 2,442,118Donal, Jr., et al.- May 25, 1948 2,459,030 Jonas et al. Jan. 11, 1949

